Convert - SMF 2.0.2 to XenForo 1.1.3

On my board users are using polish language. I tried to convert my board from SMF 2.0.2 to XenForo 1.1.3. Of course I can't do it directly so I used IP Board - 3.2.3. Unfortunately, in posts, threads, almost in everything that is related with database, where are polish alphabet's characters like "ą,ę,ó" etc. appeard question marks. What can I do to avoid this?